Electrically conductive lead and a method of producing such a lead

ABSTRACT

In an electrically conductive lead adapted for implantation in a human or animal body, and a method for making such a lead, a drug-dispensing member is disposed at a distal end portion of the lead, at which an electrode member is disposed that is adapted to emit and/or sense electrical signals associated with medical therapy. The drug-dispensing member has a configuration so that, after implantation, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from al larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to leads which are electrically conductive and which are suitable to be implanted in a human or animal body. Such leads may for example be used to conduct electrical stimulation pulses from an implanted heart stimulating device to the heart of said human or animal body. Leads may, however, also be used in connection with other kinds of medical devices. Preferably the heart electrode leads are adapted to be insertable via the vascular system into the human or animal heart. Such heart electrode leads are particularly suitable for intracardial stimulation of the heart with the help of an implantable pacemaker or defibrillator. The invention concerns both a lead as such and a method of producing a lead.

[0003] 2. Description of the Prior Art

[0004] A large number of different leads are known in the art. A lead normally has a proximal end portion to be connected to a device, for example a heart-stimulating device, and a distal end portion that is to be positioned at a predetermined position in the body, usually in or at the heart. A heart electrode lead may be unipolar or bipolar. A unipolar lead has only one single electrode member usually arranged at the tip of the distal end portion of the lead. A bipolar lead has two electric poles. Also this kind of electrode lead usually has one electrode member located at the tip at the distal end portion of the lead. -The lead has at least one electric conductor, which extends from the proximal end portion to the electrode member at the distal end portion.

[0005] For example in case of a lead for a heart stimulating device, it is known that when a lead has been implanted into or at the heart, the stimulation threshold is higher during a certain time after the implantation and then becomes lower. It is also known that this stimulation threshold may be lowered by providing a drug, such as a steroid, at the distal end portion of the lead. The drug is arranged such that it will be dispensed to the surrounding body tissue over a period of time.

[0006] U.S. Pat. No. 5,103,837 describes that a coating including a drug is provided on an electrode member of titanium nitride.

[0007] U.S. Pat. No. 4,819,661 describes different leads with helical fixation members. A drug impregnated matrix, preferably of a biocompatible silicon adhesive, is positioned in a cavity at the distal end portion of the lead.

[0008] U.S. Pat. No. 5,003,992 also describes a lead with a helical fixation member. A plug made of a polymer with a drug is located in a cavity at the distal end portion of the lead.

[0009] U.S. Pat. No. 5,002,067 discloses a lead with a helical fixation member. A cylindrical plug fabricated of a silicon-based polymer incorporating an anti-inflammatory drug is positioned in a cavity at the distal end portion of the lead. The fixation helix may also be provided with a groove -along which the drug may be released.

[0010] U.S. Pat. No. 4,972,848 describes a lead with a helical fixation means. A release device made of a polymer and incorporating a drug is provided in a cavity at the distal end portion of the lead.

[0011] U.S. Pat. No. 4,506,680 describes a sintered metal electrode member located at the distal end of the lead. In a cavity inside of this electrode member a polymer impregnated with a drug is positioned.

[0012] U.S. Pat. No. 4,577,642 describes a lead with a porous sintered metal electrode member located at the distal end portion of the lead. In a cavity inside of the electrode member, a drug is retained in a solid plug or a powder wherein the drug is compounded with an appropriate molecular sieve material.

[0013] U.S. Pat. No. 6,038,482 discloses a lead with an electrode member positioned at the distal end portion of the lead. The electrode member has an interior cavity and a bore extending between the interior cavity and the exterior surface of the electrode member. A matrix member with a drug is positioned in the interior cavity. The exterior surface of the electrode member is coated with a wetting agent with the same drug as in the matrix. Also the bore is filled with a wetting agent with the same drug as in the matrix. According to this document, a tiered delivery of the drug is achieved, where the drug on the exterior surface and in the bore elutes within approximately a 24 hour period and the drug in the matrix elutes for a much longer term measured in months or years.

[0014] U.S. Pat. No. 4,819,662 describes a cardiac pacing lead that includes a porous platinum tip electrode that can be loaded with a drug that will be eluted upon implantation. One or several matrices can be housed in a recess behind the tip electrode for continous drug elution.

[0015] EP-A-0 334 306 describes a transdermal adhesive for diminishing release of active substances.

SUMMARY OF THE INVENTION

[0016] One object of the present invention is to provide a lead that includes a drug and that is arranged such that an efficient utilisation of the drug is achieved. A second object is to provide a method of producing such a lead.

[0017] Further advantages of the present invention will become clear from the following description.

[0018] The first object of the invention is achieved by an electrically conductive lead suitable to be implanted in a human or animal body, the lead comprising:

[0019] a proximal end portion designed to be attached to a device,

[0020] a distal end portion comprising at least one electrode member for emitting and/or sensing electrical signals,

[0021] an elongated body extending between said proximal end portion and said distal end portion,

[0022] a drug dispensing member positioned at said distal end portion and comprising a drug adapted to be released into said human or animal body, wherein the drug dispensing member is located such that a part of the surface of the drug dispensing member faces the exterior of the lead, and wherein said drug dispensing member is designed such that, once the lead has been implanted into said body, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from a larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time.

[0023] Since the drug dispensing member is designed in this manner, the drug released into the body can be controlled in an optimal way. It is thus, for example, possible to control that a certain high amount of drug is released immediately after implantation of the lead, whereafter the amount of drug released per time unit smoothly decreases in a controlled manner to a smaller amount.

[0024] According to a preferred embodiment of the lead according to the invention, said drug comprises an anti-inflammatory agent. Such a drug may for example be used to decrease the stimulation threshold for a pacemaker lead.

[0025] According to a further embodiment, the design of the drug dispensing member is such that the decrease in the amount of drug released into the body from a maximum amount released during the first hours after implantation to an amount which is about ⅓ of this maximum amount takes at least 24 hours. Such a decrease in the amount of drug released is advantageous in many cases where a lead is implanted into a body.

[0026] According to another embodiment, said distal end portion comprises at least one cavity having an opening arranged at an exterior surface of the distal end portion of the lead such that the cavity is open to the exterior of the distal end portion, wherein said drug dispensing member is located in said cavity, and wherein the shape of the cavity is such that the amount of drug released into the body per time unit is controlled by said shape. Such a lead may be made in a relatively simple manner. Since the drug dispensing member is located in the cavity, it is arranged well protected against accidental damage.

[0027] According to a further embodiment, the shape of said cavity is such that the cross-sectional area of the cavity varies smoothly from a maximum area at said opening at the exterior surface of the distal end portion to an essentially smaller area at a position further into said cavity. Such a lead is relatively easy to make and the release of the drug may thus be controlled in a simple manner. By cross-sectional area is meant the area of the cross-section perpendicular to the main direction in which the elongated lead extends.

[0028] According to a further embodiment, the shape of said cavity is such that said maximum cross-sectional area at said opening at the exterior surface of the distal end portion is at least twice the smallest cross-sectional area of said cavity. With such a design, the amount of drug released can be controlled to decrease to a predetermined amount.

[0029] According to another embodiment, said at least one electrode member comprises a first surface portion facing the exterior of the distal end portion of the lead and a second surface portion facing the interior of the lead, wherein said cavity is located such that said opening is located in said first surface portion. The drug may thus be released at the very end tip of the lead.

[0030] According to a further embodiment, said cavity is located such that the cavity does not extend to the second surface portion, such that it does not extend all the way through the electrode member, wherein the cavity does not have any opening towards the interior of the lead. Such an electrode member is relatively easy to produce. Furthermore, there is no risk that body fluids enter into the interior of the lead via the cavity.

[0031] According to still another embodiment, said cavity extends from said first surface portion and has a minimum cross-sectional area at an intermediate position of said cavity which is smaller than the cross-sectional area of the cavity at a position located proximal of said intermediate position. A larger space may in this manner be formed inside of a narrower part of the cavity. The larger space may, for example, be used to hold a drug intended for a long term release.

[0032] According to a further embodiment, said cavity is positioned such that said opening is located at the distal end tip of the lead and such that the cavity extends in the longitudinal direction of the lead. In such a lead, the cavity may be symmetrically arranged in the distal portion of the lead.

[0033] According to another embodiment, said distal end portion comprises a plurality of said cavities. The lead may thus comprise a plurality of cavities, which together are designed such that the amount of drug released is controlled to vary according to a predetermined relationship.

[0034] According to a further embodiment, said drug dispensing member or members are formed in a material that is soluble or resorbable in body fluids. Such a material is particularly suitable for holding the drug.

[0035] According to another embodiment, said electrode member forms the distal end portion of the lead and said drug dispensing member is positioned on the surface of said electrode member. In such a lead, it is not necessary to form a cavity in the electrode member.

[0036] According to a further embodiment, said drug dispensing member is formed in a material that is soluble or resorbable in body fluids and the drug dispensing member has a shape that is such that the exterior surface area of the drug dispensing member will decrease with time, when the drug dispensing member is dissolved or resorbed, in such a manner that said controlled release of the drug is achieved. Instead of a particular shape of a cavity, it is thus possible to control the release of the drug by a particular design of the drug dispensing member positioned on the surface of the electrode member.

[0037] According to a further embodiment, said drug dispensing member has a cone-like shape with a base surface attached to said electrode member and a narrow end, pointing away from said electrode member. A lead with such a drug dispensing member may be formed in a relatively simple manner.

[0038] According to a still further embodiment, said drug dispensing member comprises different concentration of said drug in different parts of the drug dispensing member such that the amount of drug released over time is controlled at least in part by the varying concentration of the drug in said member.

[0039] According to a further embodiment, different parts of the drug dispensing member comprise materials of different compositions, which are soluble or resorbable in body fluids with different pace, wherein said different parts are positioned such that the amount of drug released over time is controlled at least in part by the different compositions and the position of the different parts in said drug dispensing member. The release of the drug may thus also be controlled by the actual material composition in different parts of the drug dispensing member.

[0040] The second object of the invention is achieved by a method of producing a an electrically conductive lead suitable to be implanted in a human or animal body and comprising a drug to be released into said body with a predetermined amount as a function of time after implantation, the method comprising:

[0041] providing an electrically conductive lead having a proximal end portion designed to be attached to a device, a distal end portion, which comprises at least one electrode member for emitting and/or sensing electrical signals, and an elongated body extending between said proximal end portion and said distal end portion,

[0042] providing a drug dispensing member at said distal end portion, which drug dispensing member comprises said drug adapted to be released into said human or animal body, wherein the drug dispensing member is arranged such that a part of the surface of the drug dispensing member faces the exterior of the lead, and wherein said drug dispensing member is designed such that, once the lead has been implanted into said body, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from a larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time.

[0043] Through this method, a lead having the above-described advantages is produced. It should be noted that the method steps does not necessarily have to be performed in the order listed above. It is, of course, possible to arrange the drug dispensing member at the distal end portion before the different parts of the lead are assembled.

[0044] Different preferred manners of carrying out the method are defined in the claims 19-34. The advantages of these manners of carrying out the method are already clear from the above description in connection with the different embodiments of the lead.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045]FIG. 1 shows a schematic side view of a distal portion of a lead according to the prior art.

[0046]FIG. 2 shows a schematic side view of a proximal portion of a lead according to the prior art.

[0047]FIG. 3 shows a sectional view of a distal end portion of a lead according to the prior art.

[0048]FIG. 4 shows a schematic sectional view of an electrode member of a distal end portion of a lead according to an embodiment the present invention.

[0049]FIG. 5 shows the same view as FIG. 4 of an alternative embodiment.

[0050]FIG. 6 shows an end view of the electrode member shown in FIG. 4 and 5.

[0051]FIG. 7 shows the same view as FIG. 4 of another embodiment of the invention.

[0052]FIG. 8 shows an end view of the electrode member shown in FIG. 7.

[0053]FIG. 9 shows the same view as FIG. 4 of a further embodiment of the invention.

[0054]FIG. 10 shows an end view of the electrode member shown in FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0055]FIGS. 1-3 show different views of a lead according to the prior art. However, the general configuration of the lead according to the present invention can be the same as that of the prior art.

[0056] The lead has a proximal end portion (FIG. 2) with connecting means 10 designed to be attached to a device, for example to a heart stimulating device. Furthermore, the lead has a distal end portion (FIG. 1) comprising an electrode member 12 for emitting and/or sensing electrical signals. The shown lead is bipolar and thus has a further electrode member 14. The lead has an elongated body extending between said proximal end portion and said distal end portion, i.e. the elongated body connects the two parts of the lead shown in FIG. 1 and FIG. 2.

[0057]FIG. 3. shows a sectional view of the distal end portion of the lead according to the prior art. FIG. 3 shows that the electrode member 12 has a first surface portion 16 facing the exterior of the distal end portion and a second surface portion 18 facing the interior of the lead. The electrode member 12 may for example be made of a platinum-iridium alloy. The surface,may be coated with titanium nitride. The lead has at least one electric conductor 20 extending between the electrode member 12 and the connecting means 10. The lead also has at least one insulating member 22, for example made of silicon rubber, which encloses the electric conductor 20. The distal end portion of the lead may be provided with tines 24 to facilitate the anchoring of the electrode tip at the body tissue.

[0058] The first embodiment of the present invention will now be described with reference to FIGS. 4 and 6. As already stated above, the, general configuration of the lead may be the same as that of the prior art described above. It should be noted that the same reference numerals are used for the corresponding parts in the different figures.

[0059] The lead of the present invention is preferably of a dimension such that it is adapted to be insertable via the vascular system into a human or animal heart.

[0060]FIG. 4 thus shows an electrode member 12. The electrode member 12 has a first surface portion 16 which faces the exterior of the distal end portion of the lead. The electrode member 12 also has a second surface portion 18 facing the interior of the lead. The electrode member 12 comprises a cavity 28. The cavity 28 has an opening 30 arranged at an exterior surface of the distal end portion of the lead. The opening 30 is located at the distal end tip of the lead and the cavity 28 extends in the longitudinal direction of the lead. According to the shown embodiment the cavity 28 does not extend to the second surface portion 18. The cavity 28 does therefore not have any opening towards the interior of the lead. It should however be noted that according to an alternative embodiment, the cavity 28 could extend all the way through the electrode member 12.

[0061] A drug dispensing member 26 is arranged in the cavity 28. The drug dispensing member 26 is designed such that, when the lead has been implanted into a human or animal body, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from a larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time. According to a preferred embodiment, the amount of drug released is controlled by the shape of the drug dispensing member 26, i.e. by the shape of the cavity 28.

[0062] The drug may for example be an anti-inflammatory agent, such as a steroid, for example dexamethasone sodium phosphate. Preferably, the drug is included in a material that is soluble or resorbable in body fluids. As examples of such materials the following may be mentioned: PLA (polylactic acid), PGA (polyglycollic acid) and PDS (polydioxanone). According to one embodiment, the material may be in the form of a gel.

[0063] According to one advantageous embodiment, the drug dispensing member 26 is designed such that the decrease in the amount of drug released into the body from a maximum amount released during the first hours after implantation to an amount which is about ⅓ of this maximum amount takes at least 24 hours.

[0064] The amount of drug released may be controlled by the shape of the drug dispensing member 26, i. e. by the shape of the cavity 28. The curvature 29 of the side faces of the cavity 28 may thus be selected in order to achieve a predetermined amount of drug release. The cross-sectional area of the cavity 28 may vary from a maximum area 32 at the opening 30 to an essentially smaller, minimum cross-sectional area 34 at a position further into said cavity 28. Preferably, the maximum cross-sectional area 32 is at least twice the smallest cross-sectional area 34.

[0065] In addition to, or instead of, controlling the release of the drug by the shape of, the cavity 28, it is possible to control the amount of drug released by the concentration of the drug in different parts of the drug dispensing member 26. Thus a higher concentration of the drug may be arranged in the part of the drug dispensing member 26 located closest to the opening 30.

[0066] It is also possible to control the amount of drug released by forming the drug dispensing member 26 of different materials of different compositions in different parts of the drug dispensing member 26. For example, materials that are more quickly resolved in body fluids may be located closer to the opening 30.

[0067]FIG. 5 shows an alternative embodiment to the electrode member 12 shown in FIG. 4. FIG. 5 shows that the cavity 28 extends from the first surface portion 16 and has a minimum cross-sectional area 34 at an intermediate position of the cavity 28. This minimum cross-sectional area 34 is smaller than the cross-sectional area 36 of the cavity 28 at a position located proximal of the intermediate position. In this way an interior somewhat larger space 37 is formed. In this space 37 a larger amount of drug may be included. Since this space 37 is located inside of the major part of the cavity 28, the drug in this space 37 is suitable for long term release.

[0068]FIGS. 7 and 8 show an electrode member 12 comprising a plurality of cavities 28. In this case the electrode member 12 comprises two such cavities 28 extending around the tip of the electrode member 12. In these cavities 28 drug dispensing members 26 are positioned. Also the shape of these cavities 28 are designed such that an automatically controlled release of the drug is obtained.

[0069] In the embodiment shown in FIGS. 9 and 10, the electrode member 12 does not comprise any cavity. Instead a drug dispensing member 26 is positioned on the surface of the electrode member 12. Also in this case, the drug dispensing member 26 is formed in a material that is soluble or resorbable in body fluids. The shape of the drug dispensing member 26 is such that the exterior surface area of the drug dispensing member 26 will decrease with time, when the drug dispensing member 26 is desolved or resorbed. In the shown embodiment the drug dispensing member 26 has a cone-like shape with a base surface 38 attached to the surface of the electrode member 12 and a narrow end 40 pointing away from the electrode member 1-2.

[0070] In a method according to the invention the lead is formed by providing the parts necessary for forming an electrically conductive lead having a proximal end portion designed to be attached to a device, a distal end portion, comprising at least one electrode member 12, and an elongated body extending between the proximal end portion and the distal end portion. A drug dispensing member 26 is provided at the distal end portion. The drug dispensing member 26 comprises a drug. The drug dispensing member 26 is designed such that the drug released into the body per time unit is automatically controlled to smoothly vary with time in accordance with a predetermined relationship such as has been described above.

[0071] The drug dispensing member may be designed by first determining a desired relationship between the amount of drug released and time after implantation, and then designing the drug dispensing member such that said relationship will be fulfilled when the lead has been implanted.

[0072] The drug preferably comprises an anti-inflammatory agent. According to the different preferred embodiments of the method, the lead with the drug dispensing member 26 is designed to have the features described above.

[0073] The invention is not limited to the above described embodiments but may be varied within the scope of the following claims. 

1. An electrically conductive lead suitable to be implanted in a human or animal body, the lead comprising: a proximal end portion designed to be attached to a device, a distal end portion comprising at least one electrode member (12) for emitting and/or sensing electrical signals, an elongated body extending between said proximal end portion and said distal end portion, a drug dispensing member (26) positioned at said distal end portion and comprising a drug adapted to be released into said human or animal body, wherein the drug dispensing member (26) is located such that a part of the surface of the drug dispensing member faces the exterior of the lead, and wherein said drug dispensing member (26) is designed such that, once the lead has been implanted into said body, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from a larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time.
 2. An electrically conductive lead according to claim 1, wherein said drug comprises an anti-inflammatory agent.
 3. An electrically conductive lead according to claim 1 or 2, wherein the design of the drug dispensing member (26) is such that the decrease in the amount of drug released into the body from a maximum amount released during the first hours after implantation to an amount which is about ⅓ of this maximum amount takes at least 24 hours.
 4. An electrically conductive lead according to any of the preceding claims, wherein said distal end portion comprises at least one cavity (28) having an opening (30) arranged at an exterior surface of the distal end portion of the lead such that the cavity (28) is open to the exterior of the distal end portion, wherein said drug dispensing member (26) is located in said cavity (28), and wherein the shape of the cavity (28) is such that the amount of drug released into the body per time unit is controlled by said shape.
 5. An electrically conductive lead according to claim 4, wherein the shape of said cavity (28) is such that the cross-sectional area of the cavity varies smoothly from a maximum area (32) at said opening (30) at the exterior surface of the distal end portion to an essentially smaller area (34) at a position further into said cavity (28).
 6. An electrically conductive lead according to claim 5, wherein the shape of said cavity (28) is such that said maximum cross-sectional area (32) at said opening (30) at the exterior surface of the distal end portion is at least twice the smallest cross-sectional area (34) of said cavity (28).
 7. An electrically conductive lead according to any of claims 4-6, wherein said at least one electrode member (12) comprises a first surface portion (16) facing the exterior of the distal end portion of the lead and a second surface portion (18) facing the interior of the lead, wherein said cavity (28) is located such that said opening (30) is located in said first surface portion (16).
 8. An electrically conductive lead according to claim 7, wherein said cavity (28) is located such that the cavity (28) does not extend to the second surface portion (18), such that it does not extend all the way through the electrode member (12), wherein the cavity (28) does not have any opening towards the interior of the lead.
 9. An electrically conductive lead according to claim 7 or 8, wherein said cavity (28) extends from said first surface portion (16) and has a minimum cross-sectional area (34) at an intermediate position of said cavity (28) which is smaller than the cross-sectional area (36) of the cavity (28) at a position located proximal of said intermediate position.
 10. An electrically conductive lead according to any of claims 4-9, wherein said cavity (28) is positioned such that said opening (30) is located at the distal end tip of the lead and such that the cavity (28) extends in the longitudinal direction of the lead.
 11. An electrically conductive lead according to any of claims 4-10, wherein said distal end portion comprises a plurality of said cavities (28).
 12. An electrically conductive lead according to any of claims 4-11, wherein said drug dispensing member or members (26) are formed in a material that is soluble or resorbable in body fluids.
 13. An electrically conductive lead according to any of claims 1-3, wherein said electrode member (12) forms the distal end portion of the lead and wherein said drug dispensing member (26) is positioned on the surface of said electrode member.
 14. An electrically conductive lead according to claim 13, wherein said drug dispensing member (26) is formed in a material that is soluble or resorbable in body fluids, and wherein the drug dispensing member (26) has a shape that is such that the exterior surface area of the drug dispensing member (26) will decrease with time, when the drug dispensing member (26) is dissolved or resorbed, in such a manner that said controlled release of the drug is achieved.
 15. An electrically conductive lead according to claim 14, wherein said drug dispensing member (26) has a cone-like shape with a base surface (38) attached to said electrode member (12) and a narrow end (40), pointing away from said electrode member (12).
 16. An electrically conductive lead according to any of the claims 1-15, wherein said drug dispensing member (26) comprises different concentration of said drug in different parts of the drug dispensing member (26) such that the amount of drug released over time is controlled at least in part by the varying concentration of the drug in said member (26).
 17. An electrically conductive lead according to any of the claims 1-16, wherein different parts of the drug dispensing member (26) comprise materials of different compositions, which are soluble or resorbable in body fluids with different pace, wherein said different parts are positioned such that the amount of drug released over time is controlled at least in part by the different compositions and the position of the different parts in said drug dispensing member (26).
 18. A method of producing a an electrically conductive lead suitable to be implanted in a human or animal body and comprising a drug to be released into said body with a predetermined amount as a function of time after implantation, the method comprising: providing an electrically conductive lead having a proximal end portion designed to be attached to a device, a distal end portion, which comprises at least one electrode member (12) for emitting and/or sensing electrical signals, and an elongated body extending between said proximal end portion and said distal end portion, providing a drug dispensing member (26) at said distal end portion, which drug dispensing member (26) comprises said drug adapted to be released into said human or animal body, wherein the drug dispensing member (26) is arranged such that a part of the surface of the drug dispensing member (26) faces the exterior of the lead, and wherein said drug dispensing member (26) is designed such that, once the lead has been implanted into said body, the amount of drug released into the body per time unit is automatically controlled to smoothly vary with time from a larger amount to a smaller amount in accordance with a predetermined relationship of the amount of drug released as a function of time.
 19. A method according to claim 18, wherein said drug comprises an anti-inflammatory agent.
 20. A method according to any of claims 18 and 19, wherein said relationship is determined such that the decrease in the amount of drug released into the body from a maximum amount released during the first hours after implantation to an amount which is about ⅓ of this maximum amount takes at least 24 hours.
 21. A method according to any of the claims 18-20, comprising the step of forming said distal end portion such that it comprises at least one cavity (28) having an opening (30) arranged at an exterior surface of the distal end portion of the lead such that the cavity (28) is open to the exterior of the distal end portion, and positioning said drug dispensing member (26) in said cavity (28), wherein the shape of the cavity (28) is designed such that the amount of drug released into the body per time unit is controlled by said shape.
 22. A method according to claim 21, comprising the step of forming said cavity (28) such that the shape of said cavity (28) is such that the cross-sectional area of the cavity (28) varies smoothly from a maximum area (32) at said opening (30) at the exterior surface of the distal end portion to an essentially smaller area (34) at a position further into said cavity (28).
 23. A method according to claim 22, wherein the shape of said cavity (28) is formed such that said maximum cross-sectional area (32) at said opening (30) at the exterior surface of the distal end portion is at least twice the smallest cross-sectional area (34) of said cavity (28).
 24. A method according to any of claims 21-23, wherein said at least one electrode member (12) is formed such that it comprises a first surface portion (16) facing the exterior of the distal end portion of the lead and a second surface portion (18) facing the interior of the lead, wherein said cavity (28) is located such that said opening (30) is located in said first surface portion (16).
 25. A method according to claim 24, wherein said cavity (28) is formed such that the cavity (28) does not extend to the second surface portion (18), such that it does not extend all the way through the electrode member (12), wherein the cavity (28) does not have any opening towards the interior of the lead.
 26. A method according to claim 24 or 25, wherein said cavity (28) is formed such that it extends from said first surface portion and has a minimum cross-sectional area (34) at an intermediate position of said cavity which is smaller than the cross-sectional area (36) of the cavity (28) at a position located proximal of said intermediate position.
 27. A method according to any of claims 21-26, wherein said cavity (28) is formed such that said opening (30) is located at the distal end tip of the lead and such that the cavity (28) extends in the longitudinal direction of the lead.
 28. A method according to any of claims 21-27, wherein said distal end portion is formed to comprise a plurality of said cavities (28).
 29. A method according to any of claims 21-28, wherein said drug dispensing member or members (26) are formed in a material that is soluble or resorbable in body fluids.
 30. A method according to any of claims 18-20, wherein said electrode member (12) is formed to constitute the distal end portion of the lead and wherein said drug dispensing member (26) is positioned on the surface of said electrode member (12).
 31. A method according to claim 30, wherein said drug dispensing member (26) is formed in a material that is soluble or resorbable in body fluids, and wherein the drug dispensing member (26) is formed to have a shape that is such that the exterior surface area of the drug dispensing member (26) will decrease with time, when the drug dispensing member (26) is dissolved or resorbed, in such a manner that said controlled release of the drug is achieved.
 32. A method according to claim 31, wherein said drug dispensing member (26) is formed to have a cone-like shape, with a base surface (38) attached to said electrode member (12) and a narrow end (40), pointing away from said electrode member (12).
 33. A method according to any of the claims 18-32, wherein said drug, dispensing member (26) is formed such that it comprises different concentration of said drug in different parts of the drug dispensing member (26) such that the amount of drug released over time is controlled at least in part by the varying concentration of the drug in said member (26).
 34. A method according to any of the claims 18-33, wherein said drug dispensing member (26) is formed such that different parts of the drug dispensing member (26) comprise materials of different compositions, which are soluble or resorbable in body fluids with different pace, wherein said different parts are positioned such that the amount of drug released over time is controlled at least in part by the different compositions and the position of the different parts in said drug dispensing member (26). 